1. Field of the Invention
The present invention relates to high-frequency signal transmission lines and electronic devices, and more particularly, the present invention relates to a high-frequency signal transmission line for use in high-frequency signal transmission and an electronic device including the same.
2. Description of the Related Art
As an invention relevant to a conventional high-frequency signal transmission line, a high-frequency signal line described in, for example, International Publication WO 2012/074100 is known. FIG. 37 is a cross-sectional structure view of the high-frequency signal line 500 described in International Publication WO 2012/074100.
The high-frequency signal line 500 includes a dielectric element assembly 512, a high-permittivity layer 515, a signal line 520, and ground conductors 522 and 524. The dielectric element assembly 512 is formed by laminating a plurality of dielectric sheets. The signal line 520 is provided in the dielectric element assembly 512. The ground conductor 522 is positioned on the positive side in the z-axis direction relative to the signal line 520. The ground conductor 524 is positioned on the negative side in the z-axis direction relative to the signal line 520. The ground conductor 524 has openings 530 provided therein. The high-permittivity layer 515 is positioned on the principal surface of the dielectric element assembly 512 that is located on the negative side in the z-axis direction. The high-permittivity layer 515 has a higher specific permittivity than the dielectric element assembly 512.
In the high-frequency signal line 500 thus configured, the high-permittivity layer 515 covers the openings 530. Accordingly, more electromagnetic field radiation from the signal line 520 is reflected into the high-frequency signal line 500 at the interface between the high-permittivity layer 515 and the air space, resulting in reduced spurious radiation.
Incidentally, in the case of the high-frequency signal line 500, if the specific permittivity of the high-permittivity layer 515 is increased, the characteristic impedance of the high-frequency signal line 500 might deviate from a desired impedance value (e.g., 50Ω). More specifically, from the viewpoint of reducing spurious radiation, the high-permittivity layer 515 preferably has a high specific permittivity. However, in the case where the specific permittivity of the high-permittivity layer 515 is high, if there is a metallic body or the like near the opening 530, high capacitance is generated between the signal line 520 and the metallic body or the like. As a result, the characteristic impedance of the high-frequency signal line 500 becomes lower than the desired impedance value.